Alkadienes: what they are, examples and isoprene

Alkadienes or dienes are open carbon chain hydrocarbons that have two double bonds.

Generally speaking, the formula for alkadienes is Ç_noH_2n-2.

Classification

Alkadienes are classified according to the position of their unsaturation:

• Accumulated dienes: The two double bonds occur on neighboring carbons.
• isolated dienes: The two double bonds belong to different carbons, in addition to being separated by at least two single bonds or a saturated carbon.
• Conjugated dienes: Double bonds appear alternately.

Examples:

1. Propadiene or but-1,2-diene (Accumulated Diene)

2. Pent-1,4-diene (isolated diene)

3. But-1,3-diene (Conjugated Diene)

How is the nomenclature given to alkadienes?

The nomenclature of alkadienes is similar to that of alkenes.

The prefixes are the same as those used in hydrocarbon nomenclature. In this case, we have the following order:

Prefix + dien + o

The term dien represents the presence of double double bonds.

The main chain is the longest and has the two double bonds. Each of the links must be numbered.

Carbon numbering starts from the end closest to the unsaturation.

Furthermore, the numbering must be carried out so that the position of double bonds and branches is as small as possible.

Examples:

1. propadiene

2. pent-1,3-diene

When alkadienes have ramifications, they should also be indicated.

Examples:

1. 5,5-dimethyl-1,2-hexadiene

2. 2-methyl-but-1,3-diene

Learn more, read also:

• Hydrocarbons
• Aromatic hydrocarbons
• carbon chains
• Organic chemistry

Isoprene

Isopropene (C₅H₈) is the most representative alkadiene, characterized as a colorless and volatile organic substance. It is represented as follows:

The carbon chain representing isoprene results in the following nomenclature: 2-methylbut-1,3-diene.

From various combinations between them, terpenes are formed, a set of substances, which stand out: natural rubber, essential oils, carotenoids and steroids.

The synthetic rubber used in the manufacture of many products is the result of the polymerization of isoprene.

Read too:

• Carbon
• alkanes
• alkenes
• Alkynes